Responding to "subtext" is essentially about reading between the lines. Listening for the "real intention or meaning" the words are trying to convey. It's like when your spouse or friend says, "My day was okay," with a sigh. Chances are they did NOT have a good day.
But, it's not always easy. I get that.
And kids are generally not good at stating what they want or need clearly and leave lots of room for "reading between the lines"....with some exceptions like, "I want a [insert your child's favourite electronic game here]."
So, what's the best way to learn to practice listening for subtext?
Try something where there's no "risk" to get it wrong, like your favourite TV show. Listen to the lines and listen for subtext in the conversations. Since it's not the words that convey "subtext" (the words are the "text", after all!), pay attention to what gives you the clues you need. Think about tone, volume, or pitch of voice. Vocal inflections and rate of speech. Body language including posture, gestures and facial expressions. And remember, it's the subtext that tells the "emotional story" that's underlying the words.
Then try to apply what you learn to "reading between the lines" with your child.